Ensure same random coordinates do not appear twice

I am simulating a grid of 200*200 cells. I am doing this by creating two arrays of random numbers, and plotting them in a scatterplot.

x=randi(200,1,1000);

y=randi(200,1,1000);

figure(1);scatter(x,y);

what I am trying to do is add something additional, if any of these random coordinates are the same, then create additional x&y values that are not the same, for whenever this occurs. To ensure that the same coordinates do not appear twice at any time.

[Stephan]

See my answer.

I looked at the questions you asked here so far. You can accept and / or vote for helpful answers in order to help people with similar Problems find helpful answers.

Also this is somehow a thank you to the volunteer contributers here, which get reputation by accepted answers.

Best regards

Stephan

[Star Strider]

See also: Setting up parasite model.

Answer 1

[Stephan]

Hi,

use randperm for getting unique values:

For p = randperm(n,k), p contains k unique values. randperm performs k-permutations (sampling without replacement). To allow repeated values in the output (sampling with replacement), use randi(n,1,k).

randperm uses the same random number generator as rand, randi, and randn. You control this generator with rng.

Best regards

Stephan

Answer 2

[Image Analyst]

Try this:

numCellsWide = 200;
numCellsOccupied = 1000;
[x, y] = meshgrid(1:numCellsWide, 1:numCellsWide);
indexes = randperm(numCellsWide * numCellsWide, numCellsOccupied);
x = x(indexes);
y = y(indexes);
plot(x, y, 'b.', 'MarkerSize', 18);
grid on;
xlabel('x', 'FontSize', 20);
ylabel('y', 'FontSize', 20);
caption = sprintf('%d points', numCellsOccupied);
title(caption, 'FontSize', 20);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);

Answer 3

[Bruno Luong]

You can do by rejection

margin = 1.2;
n = 1000;
xy = [];
mxy = 0;
while mxy < n
    m = ceil(margin*n)-mxy;
    xy = unique([xy; randi(200,m,2)],'rows');
    mxy = size(xy,1);
end
x = xy(1:n,1);
y = xy(1:n,2);

or direct method

n = 1000;
i = randperm(200*200,n);
[x,y] = ind2sub([200 200], i);